| Issue |
A&A
Volume 647, March 2021
|
|
|---|---|---|
| Article Number | A127 | |
| Number of page(s) | 13 | |
| Section | Atomic, molecular, and nuclear data | |
| DOI | https://doi.org/10.1051/0004-6361/202039985 | |
| Published online | 22 March 2021 | |
Photodissociation branching ratios of 12C16O from 110 500 to 113 045 cm−1: first observation of the C(1S) channel★
1
Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences,
Beijing
100190,
PR China
2
University of Chinese Academy of Sciences,
Beijing
100049,
PR China
e-mail: honggao2017@iccas.ac.cn; chengmin@iccas.ac.cn
Received:
25
November
2020
Accepted:
25
January
2021
Carbon monoxide (CO) is one of the most abundant molecular species in comets. Its photodissociation by the solar radiation in the vacuum ultraviolet (VUV) region produces excited atomic fragments C(1D), C(1S), and O(1D), which radiate at characteristic wavelengths when they decay to lower states. The fractional rate constants for generating these fragments from CO photodissociation under the entire range of the solar radiation field are key input values in modelling the observed atomic emission intensities from comets. In this study, the branching ratios of the four lowest dissociation channels C(3P)+O(3P), C(1D)+O(3P), C(3P)+O(1D), and C(1S)+O(3P) of the 12C16O photodissociation are measured in the VUV energy range between the threshold of producing the C(1S)+O(3P) channel (~110 500 cm−1) and the ionisation energy (IE) of 12C16O (~113 045 cm−1). We measured these ratios using the VUV time-slice velocity-map ion imaging apparatus. We observe a number of high Rydberg states in the aforementioned energy range, with most of them mainly producing ground C(3P) and O(3P) atomic fragments, and only a few of them producing a significant amount of excited C(1D) or O(1D) fragments. We also observe the excited C(1S) fragment from CO photodissociation and measured its branching ratio for the first time. Based on the photodissociation branching ratios measured in the current and previous studies, we are able to estimate the relative percentages of the excited atomic fragments C(1D), C(1S), and O(1D) from the solar photolysis of 12C16O below its IE. We discuss the implications for the photochemical modelling of the CO-dominated comet C/2016 R2 (Pan-STARRS).
Key words: molecular data / comets: general / planets and satellites: atmospheres / Sun: UV radiation / ISM: molecules
The C+ ion photofragment spectrum is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/647/A127
© ESO 2021
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.